1. Field of the Invention
The present invention relates to an oscillation detecting apparatus for detecting the oscillation of a signal and a test apparatus for testing an electronic device.
2. Description of the Related Art
Conventionally, in a test apparatus for testing an electronic device such as a semiconductor circuit, a source power is supplied to the electronic device. In some cases, the power supply voltage may oscillate according to the characteristics of the electronic device connected to the test apparatus as a load. When the power supply voltage oscillates, it is desirable to detect the oscillation of the power supply voltage because there is concern that the test apparatus or the electronic device might be damaged.
A conventional oscillation detecting apparatus includes a filter for removing a direct current component of a given signal, an absolute value circuit for rectifying the signal, an integration circuit for integrating a waveform of the rectified signal and a determination circuit for determining whether or not a signal is in oscillation according to the integration value.
However, the oscillation detecting apparatus of such a configuration may detect the signal, whose amplitude is large, as if it is in oscillation, even though it is not in oscillation, because the integration value of the signal becomes large.
For example, in a test apparatus, when the fluctuation of a signal level is large, e.g. the output of the power supply voltage is started or stopped, the amplitude of the output signal of a filter in the oscillation detecting apparatus becomes large, so that the oscillation detecting apparatus detects the oscillation incorrectly.